Threaded plastic closures for containers, such as for carbonated beverages and the like, have found very widespread acceptance in the marketplace. Closures of this nature typically include a molded plastic closure cap having a top wall portion, and a depending cylindrical skirt portion. The skirt portion includes an internal thread formation configured for threaded cooperation with a like thread formation on an associated container. The desired sealing with the container can be achieved by providing the closure with a sealing liner positioned generally adjacent the top wall portion. Closures of this type which have proven to be particularly commercially successful are disclosed in U.S. Pat. No. 4,343,754, No. 4,378,893, and No. 4,497,765, all of which are hereby incorporated by reference. For many applications, it is desirable to configure such closures for tamper-indication, such as in accordance with the teachings of the above-referenced U.S. Pat. No. 4,497,765, or in accordance with the teachings of U.S. Pat. No.4,938,370, No. 4,978,017, and No. 5,004,112, all hereby incorporated by reference.
As noted, closures of the above type have proven to be very commercially successful for use on containers having carbonated contents. As such, closures of this type are typically configured to facilitate venting and release of gas pressure from within the container during closure removal. In particular, it is desirable to release such gas pressure from within the container prior to disengagement of the closure thread formation from the threads provided on the neck portion of the associated container.
While it has long been recognized that gas can flow from within the container, during closure removal, by flow along the mating thread formations, other arrangements have been employed to facilitate gas flow. Such arrangements include the provision of vent grooves in the container, which grooves are generally axially oriented, and traverse and substantially interrupt the container thread formation. Similarly, the threads of a closure can be interrupted to provide increased gas flow, with the provision of axially extending vent grooves in the side wall of closures also known.
Experience has shown that use of interrupted threads and/of vent grooves in plastic closures can sometimes detract from optimum closure performance. While efforts have been made in the past to maximize the cross-sectional area of such closure vent passages, it is desirable to maximize the length of each individual closure thread between the vents to maximize axial strength and hoop strength of the closure. Additionally, short thread segments have been shown to contribute to misapplication of closures during high-speed bottling, by contributing to "cocking" or misaligned application of closures. It is also believed to be desirable to limit the depth of such closure vent passages, to thereby minimize any decrease in strength of the closure in such regions. It is believed that reduction in the closure wall thickness in the vent locations can result in the formation of "knit/weld lines" during the closure molding process. Molten plastic material naturally tends to seek the flow path of least resistance as the mold space is filled during the closure molding process. As a consequence, areas in which the closure wall thickness is reduced (i.e., at closure vent passages) which are bordered by areas of increased wall thickness may not fill as quickly as the thicker adjacent regions. The resulting knit/weld lines formed axially in the region of the vent passages naturally exhibit reduced strength, and can undesirably detract from the impact resistance of such closures.
In light of the above, it is believed that it is desirable to minimize the number of vent passages provided in a threaded plastic closure, while preferably also maximizing the length of individual thread segments between vent passages. In this regard, it has been known in the prior art to provide plastic closures with projections on or adjacent to the thread formation, which projections act to inhibit relative rotation of the closure with respect to the container. These projections, sometimes referred to as "speed bumps", can coact with the thread formation of the container to inhibit relative rotation, and may further inhibit such rotation by coaction with axially extending vent grooves of the container. Inhibiting closure rotation during removal facilitates venting of gas pressure from within the container prior to disengagement of the mating thread formations.
While such rotation-inhibiting projections are known, their use can also complicate closure application. The engagement of such a projection with the associated container thread during high-speed application can also undesirably result in "cocking" of closures, thus detracting from efficient high-speed bottling.
The present invention is directed to a closure having an improved arrangement of rotation-inhibiting projections which facilitate release of gas pressure within an associated container prior to disengagement of the cooperating closure and container thread formations.